Enzymatic unhairing and dewooling process



United Sttes Patent 2,857,316 Patented Oct. 21, 1958 ENZYMATIC UNHAIRING AND DEWOOLING PRQCESS Otto Grimm, Darrnstadt, Germany, assignor to Rohm & Haas G. m. b. H., Darmstadt, Germany N Drawing. Application September 8, 1955 Serial No. 533,227

Claims priority, application Germany March 30, 1955 7 Claims. (Cl. 195-6) The present invention relates to a or dewooling skins and hides.

The unhairing or dewooling of hides incidental to the preparation of leather has a history almost as old as civilization itself. The classic method of treating skins and hides in order to facilitate removal of the hair or wool therefrom with a minimum of attack on the fibrous part of the hide, which consists of collagen and is the material that is made into leather, has been that of soaking the hide in an aqueous lime solution. This process, however, is extremely slow in that it requires soaking for periods of one to four weeks. This liming process has been accelerated to reduce the time required to the order of one or several days by adding so-called Sharpeners. These are primarily sulfides such as sodium sulfide, sodium hydrosulfide and arsenic sulfide, but also include amines such as dimethylamine.

It has also been proposed heretofore to accomplish the unhairing in an aqueous solution containing an enzyme, the amount of Water employed being in the neighborhood of 300 to 500% by weight based on the weight of softened hides. As recently as 1941 it has been proposed, in U. S. Patent 2,229,420 to Neugebauer, to accomplish the unhairing of hides in aqueous baths containing a water-soluble sulfite, a small concentration of a water-soluble salt of a heavy metal and a proteolytic enzyme. It is a general practice in the leather making art to treat hides and skins for unhairing by submersion for periods of time ranging from days to several weeks, depending upon the particular chemical agents used.

The practice of employing enzymes in aqueous solution was based on an assumption that the liming or hair loosening process is a biochemical phenomenon which can take place only in solution and on the fact that the enzymes available on the market for depilation are, probably without exception, mixed with a carrier substance, usually kaolin, and adsorptively bound thereto. The concentration of enzyme in the commercial products is small, being usually only about 1% by weight. This low concentration of biochemically active materials in carrier substances which play no part in the liming or depilation process is justified because it facilitates establishing the desired concentration of enzyme in the treating liquor. At the same time, the enzymes are extensively protected from the action of moisture and thus stabilized when they are mixed with materials such as kaolin. Because of the small concentration of enzymes in commercial products, it appeared expeditious to introduce the enzymecontaining product into the lime or hair loosening liquor and to dissolve the enzymes by means of relatively large quantities of water to effectively remove them from the carrier substance and thus permit them to exert their full action on the hide to be treated.

It is also general knowledge within the art that enzymatic depilation as practiced heretofore has not led to uniformly satisfactory results. Thus, for example, the enzymatic unhairing of calfskins and dewooling of fresh, un-

method of unhairing '2 cured sheepskins or of dried and salted sheepskins has not been adopted on a large scale.

The surprising discovery has now been made that fresh, uncured, dried, salted, and soaked hides and skins, including calfskins and sheepskins, canbe unhaired or dewooled most advantageously with the aid of a proteolytic enzyme by applying enzyme to the skin or hide in powder form.

In contrast with enzymatic depilation and dewooling processes heretofore proposed, which involve immersion of the skins and hides in a bath containing the enzyme, the treatment in accordance with this invention has the advantage of being eifective at ambient temperatures of the order of 18 to 20 C. Enzyme-containing baths are relatively ineffective at such temperatures. A further important advantage of the method of the invention is the ability to use presently available commercial products containing enzymes in small but effective concentrations of the order of about 1%.

The enzymes that are highly effective in the method of the invention include the afore-mentioned commercial products containing proteolytic enzymes obtained with the aid of molds and bacteria and also pancreatic enzymes. The mold tryptases, and particularly those formed by Aspergillus strains have proven to be extremely effective and are, therefore, preferred. Bacterial proteases are next in the order of effectiveness and preference. If they are used in place of mold tryptases, it is generally necessary to employ a greater amount of enzyme or else to allow the enzyme to act for a longer period of time. Pancreatic enzymes, e. g., pancreas tryptase, are also suitable but somewhat less effective. Their utility is of particular interest and importance because of the inability heretofore to achieve any useful depilation with pancreas tryptase-containing baths without preliminary alkaline swelling. However, at least about three times as much as the enzyme from pancrease tryptase must be employed as compared with mold tryptase in order to achieve approximately equivalent results. If desired, the effectiveness of the enzymes employed may be still further increased by the addition thereto of carbohydrases.

As a guide to those skilled in the art, the use of powdered mold tryptase products in amounts ranging between about 100 and about 140 grams per square meter of hide insures uniformly satisfactory results. Thus, for example, for dewooling a sheepskin of average size, i. e., about /4 square meter in area, the application thereto of approximately to grams of the powdered enzyme is most effective.

The enzymes can be used alone or together with activating agents such as reductive sulfur compounds, nitrates and nitrites. Ammonium salts and preservatives may also be used with advantage. it is to be emphasized, however, that entirely satisfactory results are obtainable without the addition of any special activatin agents and that this is true particularly of the treatment of raw hides, e. g., green sheepskins, which have heretofore been difficult to treat euzymaticaily.

When working with dried, untreated hides, it is gen erally advantageous to soak them in solutions containing bacterial proteases and then, after the soaking has been completed, to sprinkle the hide, preferably on the flesh side, with an enzyme product having a mold tryptase base. The unhairing can take place immediately after a suitable storage period. Skins that have been powdered with the enzyme preparation may, if desired, also be imersed in water after a few hours of storage and then unhaired or dewooled.

The unhaired or dewooled skins obtained in accordance with the method of the invention may be aftertreated in the customary manner in an alkaline swelling liquor or with caustic alkali. After-treatment with caustic alkali results in particularly clean depilated hides and in uniformly dyeable leathers.

The utility and advantages of the method of the invention are further demonstrated in the following examples included to illustrate the best modes now contemplated for carrying out the invention.

Example 1 Example 2 Salted calfskins were first soaked in water and then sprinkled on the flesh side with a powdered product of Aspergillus flavus containing 10% sodium bisulfite and ammonium sulfate. The skins were unhaired. after 14 to 18 hours, rinsed and then after-treated with a fulling bath containing lime and sodium sulfide.

Example 3 Salted sheepskins were soaked in water in the customary manner. A powdered mixture of mold tryptaste and mold-manufactured carbohydrase was then sprinkled on the flesh side of the skins. After three hours storage the skins so treated were immersed in water for an addi-- tional twelve hours, after which dewooling was easily accomplished.

Example 4 Dried goatskins were enzymatically soaked with the aid of mold tryptase and then sprinkled on the flesh side with a powdered mixture of mold tryptase containing 5% sodium sulfite and 5% ammonium sulfate. After lying overnight, the treated skins were readily unhaired.

Example 5 Dried sheepskins were soaked with bacterial protease and carbohydrase and in the presence of sodium bisulfite and ammonium sulfate. The flesh sides were thereupon sprinkledwith a powdered mixture of mold tryptase and sodium bisulfite. After storage overnight, the treated skins were readily dewooled.

Example 6 Salted calfskins were soaked in water. One portion was then sprinkled on the flesh side with pancreatic tryptase. Another portion was tumbled for about one hour with 2 to 3% by weight, based on the weight of the soaked skins, of the same powdered tryptase without ad- 4 dition of water. After an additional incubation period of 16 to 18 hours, both portions of the treated skins were readily unhaired.

It is to be expected that numerous modifications will readily occur to those skilled in the art upon reading this description. All such modifications are intended to be included within the scope of the invention as defined in the appended claims.

I claim:

1. A method of unhairing skins and hides which comprises applying proteolytic enzyme, in powder form, to a hide, permitting enzymatic action to take place at ambient temperature without imersion in water, and thereafter unhairing the treated hide.

2. A method of unhairing dried and salted hides which comprises presoaking the hides, applying thereto proteolytic enzyme in powder form, permitting enzymatic action to take place at ambient temperature without further immersion in water, and thereafter unhairing the treated hide.

3. A method of unhairing skins and hides which comprises applying mold tryptase, in powder form, to the flesh side of a hide, permitting enzymatic action to take place at ambient temperature without immersion in water, and thereafter unhairing the treated hide.

4. A method of unhairing skins and hides which comprises applying bacterial protease, in powder form, to the flesh side of a hide, permiting enzymatic action to take place at ambient temperature without immersion in water, and thereafter unhairing the treated hide.

5. A method of unhairing skins and hides which comprises applying pancreas tryptase, in powder form, to the flesh side of a hide, permitting enzymatic action to take place at ambient temperature without immersion in water, and thereafter unhairing the treated hide.

6. A method of unhairing skins and hides which comprises applying proteolytic enzyme and carbohydrase, in powder form, to the flesh side of a hide, permitting enzymatic action to take place at ambient temperature without immersion in water, and thereafter unhairing the treated hide.

7. A method of unhairing skins and hides which comprises presoaking the hides, applying thereto proteolytic enzyme in powder form, tumbling the hides at ambient temperature for permitting the enzyme to penetrate the hide without additional soaking, and thereafter unhairing the treated hide.

References Cited in the file of this patent UNITED STATES PATENTS 1,936,074 Tressler et al. Nov. 21, 1933 2,157,969 Rohm May 9, 1939 2,169,148 Jaeger et a1. Aug. 8, 1939 2,215,055 Rohm Sept. 17, 1950 

1. A METHOD OF UNHAIRING SKINS AND HIDES WHICH COMPRISES APPLYING PROTEOLYTIC ENZYME, IN POWDER FORM, TO A HIDE, PERMITTING ENZYMATIC ACTION TO TAKE PLACE AT AMBIENT TEMPERATURE WITHOUT IMMERSION IN WATER, AND THEREAFTER UNHAIRING THE TREATED HIDE. 